Light emitting device

ABSTRACT

A manufacturing method of an active matrix light emitting device in which the active matrix light emitting device can be manufactured in a shorter time with high yield at low cost compared with conventional ones will be provided. It is a feature of the present invention that a layered structure is employed for a metal electrode which is formed in contact with or is electrically connected to a semiconductor layer of each TFT arranged in a pixel area of an active matrix light emitting device. Further, the metal electrode is partially etched and used as a first electrode of a light emitting element. A buffer layer, a layer containing an organic compound, and a second electrode layer are stacked over the first electrode.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light emitting device with a lightemitting element that emits fluorescent light or phosphorescent lightupon application of electric field to a pair of electrodes of theelement which sandwich a layer containing an organic compound(hereinafter, an organic compound layer), and to a method ofmanufacturing the light emitting device. Further, the present inventionrelates to a deposition apparatus for forming an organic compound layeror the like.

2. Description of the Related Art

Light emitting elements, which use organic compounds as a light emittingmember and are characterized by the thinness, lightweight, fastresponse, and direct current low voltage driving, are expected to beapplied to next-generation flat panel displays. Among display devices,ones having light emitting elements arranged in matrix are considered tobe particularly superior to conventional liquid crystal display devicesfor their wide viewing angle and excellent visibility.

It is said that light emitting elements emit light through the followingmechanism: voltage is applied between a pair of electrodes that sandwichan organic compound layer, electrons injected from the cathode and holesinjected from the anode are recombined at the luminescent center of theorganic compound layer to form molecular excitons, and energy isreleased while the molecular excitons return to the base state to causethe light emitting element to emit light. Singlet excitation and tripletexcitation are known as excitation states, and it is considered thatluminescence can be conducted through either one of those excitationstates.

Such light emitting devices having light emitting elements arranged inmatrix can use passive matrix drive (simple matrix type), active matrixdrive (active matrix type), or other driving methods. However, if thepixel density is increased, active matrix drive in which each pixel (oreach dot) has a switch is considered advantageous because they can bedriven at low voltage.

Organic compounds for forming a layer containing an organic compound(strictly, light emitting layer), which is the center of a lightemitting element, are classified into low molecular weight materials andhigh molecular weight (polymer) materials. Both types of materials arebeing studied but high molecular weight materials are attracting moreattention because they are easier to handle and have higher heatresistance than low molecular weight materials.

A conventional active matrix light emitting device includes a lightemitting element in which an electrode electrically connected with a TFTover a substrate is formed as an anode, an organic compound layer isformed thereover, and a cathode is formed thereover. Light generated atthe organic compound layer can be extracted at the TFT side through theanode that is a transparent electrode.

In view of the above, the applicants suggested an active matrix lightemitting device including a light emitting element having a structure inwhich an electrode on a TFT side, which is electrically connected to aTFT over a substrate is formed as an anode, a layer containing anorganic compound is formed over the anode, and a cathode that is atransparent electrode is formed over the layer containing an organiccompound (a top emitting structure) (Reference 1: Japanese PatentLaid-Open No. 2004-6327, Reference 2: Japanese Patent Laid-Open No.2004-63461, and Reference 3: Japanese Patent Laid-Open No. 2004-31201).

The present invention provides a structure and a manufacturing method ofan active matrix light emitting device in which the active matrix lightemitting device can be manufactured in a shorter time with high yield atlow cost compared with conventional ones.

It is a feature of the present invention that a layered structure isemployed for a metal electrode which is formed in contact with or iselectrically connected to a semiconductor layer of each TFT arranged ina pixel area of an active matrix light emitting device. Further, themetal electrode is partially etched and used as a first electrode of alight emitting element. A buffer layer, a layer containing an organiccompound, and a second electrode layer are stacked over the firstelectrode.

The metal electrode to be formed in contact with the semiconductor layerof the TFT is processed and used as a first electrode; thus, the stepsof forming a first electrode can be omitted.

Further, in the invention, a first electrode obtained by partiallyetching a metal electrode may be one or two layers of a metal film in aregion which is in contact with a buffer layer (namely, a light emittingregion). In addition, three or four layers of the metal film may beformed in a region in which a contact hole which reaches a semiconductorlayer of a TFT is provided. The first electrode of the invention is notlimited to the structure in which the region having three or four layersof the metal film surrounds the light emitting region.

The first electrode of the invention has different number of layersdepending on the parts, so that steps are formed at the boundariesbetween layers having different number of layers. The steps are coveredwith an insulator (referred to as a bank, a partition wall, mound, orthe like). Incidentally, at least an upper end of the insulator iscurved to have curvature radius; the curvature radius preferably 0.2 μmto 0.3 μm. The curvature radius is provided to obtain good stepcoverage; thus, a layer containing an organic compound or the like to beformed later can be formed with extremely thin thickness.

Further, by providing a buffer layer on the metal electrode, distancebetween the first electrode and a second electrode in the light emittingelement can be increased; accordingly, a short circuit in the lightemitting element due to irregularities on the surface of the metalelectrode or the like can be prevented.

The buffer layer is a composite layer of an organic compound and aninorganic compound which can accept electrons from the organic compound.Specifically, the buffer layer is a composite layer containing a metaloxide and an organic compound.

Further, the buffer layer is preferable because of superior conductivityin addition to the effect which is considered to be obtained by addingan inorganic compound (greater heat resistance or the like).

Accordingly, the thickness of the buffer layer can be made thickerwithout increase in the drive voltage; thus, a short circuit in anelement due to dust in forming the light emitting element or the likecan be prevented, and the yield can be improved.

In a full color light emitting device having three kinds (R, G, and B)of light emitting elements, the light emission efficiency variesdepending on the emission colors. Excess current has been necessarilysupplied in a light emitting element having bad light emissionefficiency in order to balance the luminance of the whole light emittingsurface of the light emitting device, which has been imperfectioncausing acceleration of deterioration of the light emitting device.

In accordance with the present invention, by controlling the thicknessof the buffer layer, the distance between the first electrode and eachlight emitting layer is controlled by controlling the layer providedtherebetween thereby improving the light emission efficiency. Anexcellent image can be displayed with clear color light emitted fromeach light emitting element; thus, a light emitting device with lowpower consumption can be realized.

Such advantages obtained by providing a buffer layer can not be obtainedusing a conventional hole transporting layer in which an organiccompound and an inorganic compound which do not electrically affect eachother are simply mixed.

Further, the buffer layer has both characteristics of hole injecting (orhole transporting) characteristics and electron injection (electrontransporting) characteristics. Accordingly, a buffer layer may also beprovided between the layer containing an organic compound and the secondelectrode so that the first electrode, a first buffer layer, the layercontaining an organic compound, a second buffer layer, the secondelectrode may be stacked in order.

A light emitting device according to the invention includes a lightemitting element having a first electrode connected to a semiconductorlayer of a thin film transistor over a substrate having an insulatingsurface; an insulator covering an end portion of the first electrode; abuffer layer over the first electrode; a layer containing an organiccompound over the buffer layer; and a second electrode over the layer.The first electrode has a first region and a second region havingdifferent number of layers from the first region, a step is formed at aboundary between the first region and the second region, and the step iscovered with the insulator.

A light emitting device according to the invention includes a lightemitting element having a first electrode electrically connected to asemiconductor layer of a thin film transistor over a substrate having aninsulating surface; an insulator covering an end portion of the firstelectrode; a buffer layer over the first electrode; a layer containingan organic compound over the buffer layer; and a second electrode overthe layer. The first electrode has a first region and a second regionhaving different number of layers from the first region, a step isformed at a boundary between the first region and the second region, andthe step is covered with the insulator.

In any of the above structures of a light emitting device above, a lightemitting device includes a pixel area provided with the plurality oflight emitting elements and a driver circuit having a plurality of thinfilm transistors, and the driver circuit includes a wiring having a samestack as the second region.

Further in the structure of a light emitting device above, the bufferlayer is provided in contact with the first region of the firstelectrode. The buffer layer contains a composite material of an organiccompound and an inorganic compound, and the inorganic compound is one ormore selected from the group consisting of titanium oxide, zirconiumoxide, hafnium oxide, vanadium oxide, niobium oxide, tantalum oxide,chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide, andrhenium oxide. The buffer layer contains a composite material containingan organic compound having hole transporting characteristics and aninorganic compound.

In the above structure, the first electrode includes a first regionhaving a metal film indulging two layers and a second region having ametal film including four layers. Alternatively, the first electrodeincludes a first region having a metal film indulging two layers and asecond region having a metal film including three layers. Stillalternatively, the first electrode includes a first region having asingle layer metal film and a second region having a metal filmincluding two or more layers. The number of the steps can be reduced asthe number of the layers in a stack is reduced, and the totalmanufacturing time can be reduced

In each of the above structure, the first electrode has a film mainlycontaining an element selected from the group consisting of Ti, TiN,TiSi_(X)N_(Y), Al, Ag, Ni, W, WSi_(X), WN_(X), WSi_(X)N_(Y), Ta,TaN_(X), TaSi_(X)N_(Y), NbN, MoN, Cr, Pt, Zn, Sn, In, and Mo; or analloy or a compound mainly containing the above element; or a stack ofthe films.

For example, when the first electrode has a first region including asingle layer of Ti and a second region having a metal film of a stackincluding two layers (a Ti layer and Al layer), the number of the stepsfor forming a film can be reduced. In the case where the first electrodeis in contact with the drain region, the Ti film is preferable since ithas low contact resistance with a semiconductor (silicon). Further, whenan Al film is used for the metal film stacked in the second region, thefirst electrode can be a low resistance electrode.

Further, in the case of using a structure in which a first region of a Wsingle layer and a second region of a metal film having a stackincluding two layers (a W layer and an Al layer), etching can be easilyconducted since the W film and the Al film has different etching rate.

Further, in each of the above structures, the area of a light emittingarea of a light emitting element is smaller than the area of the firstregion.

Further, in each of the above structure, the second electrode is alight-transmitting conductive film.

Further, a structure of the invention for realizing the above structureincludes a method for manufacturing a light emitting device including aplurality of light emitting elements having a first electrode, a layercontaining an organic compound over the first electrode, and a secondelectrode over the layer containing an organic compound, comprising thesteps of: forming a semiconductor layer of a thin film transistor;forming an insulating film covering the semiconductor layer of the thinfilm transistor; forming an electrode formed with a stack of metallayers in contact with the semiconductor layer of the thin filmtransistor, over the insulating film; removing a part of the stack ofthe electrode to form a first region, a second region having more layersthan the first region, and a step at a boundary between the first regionand the second region; forming an insulator covering the step and thesecond region of the first electrode; forming a buffer layer in contactwith the first region; forming the layer containing an organic compoundover the buffer layer; and forming the second electrode which transmitslight over the layer containing an organic compound.

The structure of the invention is not limited to a full color displaydevice having a pixel area provided with three kinds of light emittingelements (R, G, and B). For example, a full color display device can beobtained by combining a light emitting element of white light emissionand a color filter. Alternatively, a full color display device can beobtained by combining a light emitting element of single color lightemission and a color conversion layer. A full color display device maybe manufactured using a pixel area provided with light emitting elementsof four or more colors, for example (R, G, B, and W).

The present invention further suggests a new deposition apparatus inwhich an evaporation source is moved while a substrate is moved. FIGS.7A and 7B each show an example of a deposition apparatus of theinvention.

FIG. 7A shows a deposition apparatus includes a film formation chamberprovided with an deposition shield for keeping the sublimation directionof a deposition material and a plurality of openings. The depositionmaterial is sublimated through the plurality of openings. An evaporationsource which is movable in a direction perpendicular to the movingdirection of a substrate (also referred to as a transfer direction) isprovided under the deposition shield. Further, the width Wb of thedeposition shield is longer than the substrate width Wa so that thethickness of a deposited film is uniformed.

A deposition apparatus according to the invention includes a means formoving a substrate in a first direction in a film formation chamber; adeposition shield which can control heating temperature, which is fixedto an internal wall of the film formation chamber; and an evaporationsource under the deposition shield and a means for moving theevaporation source in a second direction perpendicular to the firstdirection under the deposition shield. The deposition shield has arectangular shape having a wider width than the width Wa of thesubstrate, a plurality of openings are provided on a top surface of thedeposition shield, and a deposition material evaporated from theevaporation source is deposited to the substrate through the pluralityof openings provided on the deposition shield.

A setting chamber connected to the film formation chamber may beprovided via a gate in order to supply the deposition material to acrucible of the evaporation source. FIG. 7A shows an example ofproviding two crucibles provided on the evaporation source. However, thenumber of crucibles is not limited in particular and three or morecrucibles may be provided, or one crucible may be provided. Further, theplurality of crucibles provided on the evaporation source may beinclined so that the evaporation centers converges thereby conductingco-evaporation.

The present invention further relates to a method for manufacturing alight emitting device using the above deposition apparatus including aplurality of light emitting elements each provided with a firstelectrode, a layer containing an organic compound over the firstelectrode, and a second electrode over the layer containing an organiccompound. The substrate is moved and the evaporation source is moved ina direction perpendicular to the moving direction of the substrate in afilm formation chamber to form a layer containing an organic compoundover the first substrate.

The deposition apparatus shown in FIG. 7A can be set as one part of amulti-chamber manufacturing apparatus. In the case where the depositionapparatus shown in FIG. 7A is connected to an in-line manufacturingapparatus, it is connected to a transfer chamber in which pressure canbe reduced. In the case of using one deposition shield and oneevaporation source for one film formation chamber, the substrate ispreferably moved over the openings of the deposition shield plural timesto obtain desired film thickness.

As shown in FIG. 7B, two deposition shields may be providedperpendicularly to the moving direction of the substrate, and anevaporation source is provided on each deposition shield therebycontinuously deposit the same deposition material to form a film. Filmformation speed can be improved with the use of such a depositionapparatus. Further, nonuniformity of the film thickness of the depositeddeposition material can be reduced by moving the evaporation source. Thetwo deposition shields are provided parallel to each other with enoughdistance therebetween. Further, as to the deposition apparatus shown inFIG. 7B, a desired film thickness can be obtained without reciprocatingthe substrate above the deposition shields. Accordingly, the substratecan be moved in one direction and the deposition apparatus is preferablyapplied to an in-line manufacturing apparatus in which a plurality ofchambers are arranged and connected in series. The deposition apparatusshown in FIG. 7B can also transfer the substrate; in the case ofconnecting the deposition apparatus shown in FIG. 7B to an in-linemanufacturing apparatus, the chamber is connected between two chambersin which pressure can be reduced.

Alternatively, different deposition materials may be set on twoevaporation sources to continuously form stacked layers. For example, afirst organic compound and an inorganic compound are separately set ontwo crucibles of a first evaporation source; a substrate is moved abovethe first evaporation source so that a buffer layer is deposited on thesubstrate. Subsequently, the substrate is moved over a secondevaporation source in which a second organic compound is set on itscrucible so that a light emitting layer can be deposited on the bufferlayer.

Further, the present invention relates to another method formanufacturing a light emitting device using the above depositionapparatus, in which the light emitting device includes a plurality oflight emitting elements each provided with a first electrode, a layercontaining an organic compound on the first electrode, and a secondelectrode on the layer containing an organic compound over a substratehaving an insulating surface. The method for manufacturing a lightemitting device includes the steps of forming a semiconductor layer of athin film transistor; forming an insulating film covering thesemiconductor layer of the thin film transistor; forming an electrodeformed with a stack of metal layers in contact with the semiconductorlayer of the thin film transistor, over the insulating film; removing apart of the stack of the electrode to form a first region, a secondregion having more layers than the first region, and a step at aboundary between the first region and the second region; forming aninsulator covering the step and the second region of the firstelectrode; forming a buffer layer in contact with the first region bymoving the substrate in a film formation chamber while moving the firstevaporation source in a direction perpendicular to the moving directionof the substrate; forming the layer containing an organic compound overthe buffer layer by moving the substrate by moving the substrate in thefilm formation chamber while moving the second evaporation source in adirection perpendicular to the moving direction of the substrate; andforming the second electrode which transmits light over the layercontaining an organic compound.

Through the above manufacturing steps, the number of the manufacturingsteps can be reduced by continuously forming a buffer layer and a layercontaining an organic compound in one film formation chamber.

Note that a light emitting device in this specification means an imagedisplay device, a light emitting device and a light source (including anillumination device). In addition, the light emitting device includesall of a module in which a light emitting device is connected to aconnector such as an FPC (Flexible Printed Circuit), a TAB (TapeAutomated Bonding) tape or a TCP (Tape Carrier Package), a module inwhich a printed wiring board is provided on the tip of a TAB tape or aTCP, and a module in which an IC (Integrated Circuit) is directlymounted on a light emitting element using COG technology.

An electroluminescent element includes an anode, a cathode, and a layercontaining an organic compound creating luminescence(electroluminescence) by applying an electric field (hereinafterreferred to as an EL layer). Luminescence in an organic compoundincludes luminescence that is obtained when a singlet-excited statereturns to a ground state (fluorescence) and luminescence that isobtained when a triplet-excited state returns to a ground state(phosphorescence). A light emitting device manufactured using amanufacturing apparatus and a film formation method according to theinvention can be applied to whichever of the cases using eitherluminescence.

A light emitting element including an EL layer (an electroluminescentelement) has a structure in which the EL layer is interposed between apair of electrodes. Typically, the EL layer has a layered structure inwhich a hole transport layer, a light emitting layer, and an electrontransport layer are stacked in order. The structure provides extremelyhigh light emission efficiency, and is employed for most of lightemitting devices that are currently under research and development.

Further, the structure in which an anode, a hole injection layer, a holetransport layer, a light emitting layer, and an electron transport layerare stacked in order; or the structure in which an anode, a holeinjection layer, a hole transport layer, a light emitting layer, anelectron transport layer, and an electron injection layer are stacked inorder can be used. The light emitting layer may be doped with afluorescent pigment. All these layers can be formed of low molecularweight materials only or of high molecular weight materials only. Theterm “EL layer” in this specification is a generic term used to refer toall layers interposed between the anode and the cathode.

In a light emitting device according to the present invention, the drivemethod for screen display is not particularly limited. For example, adot-sequential driving method, a line sequential driving method, aplane-sequential driving method or the like can be employed. Typically,a line sequential driving method is employed and a time ratio grayscaledriving method or an area ratio grayscale driving method is usedsuitably. A video signal inputted to a source line of the light emittingdevice may be an analog signal or a digital signal, and driver circuitsand other circuits are designed in accordance with the type of the videosignal as appropriate.

In accordance with the present invention, in the case of a full-colorlight emitting device having three or more kinds of light emittingelements, excellent images can be displayed with clear color lightemitted from each light emitting element; thus, a light emitting devicewith low power consumption can be realized.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of an active matrix light emittingdevice (a part of a pixel) (Embodiment Mode 1);

FIGS. 2A and 2B are respectively a top view and a cross-sectional vieweach showing an example of a pixel structure of a light emitting device(Embodiment Mode 1);

FIG. 3 is a cross-sectional view of an active matrix light emittingdevice (a part of a pixel) (Embodiment Mode 2);

FIGS. 4A and 4B are respectively a top view and a cross-sectional viewof an EL module (Embodiment Mode 2);

FIGS. 5A to 5C are schematic views each showing a method of combining awhite light emitting element and a color filter (Embodiment Mode 3);

FIG. 6 is a top view of a manufacturing apparatus (Embodiment Mode 4);

FIGS. 7A and 7B are respectively a perspective view and a top view eachshowing a deposition apparatus (Embodiment Mode 4);

FIG. 8 shows measured results of relative luminance at a voltage of 6 V;

FIG. 9 shows an element structure used for the measurement;

FIGS. 10A to 10D each show an example of electronic devices; and

FIG. 11 shows an example of an electronic device.

DETAILED DESCRIPTION OF THE INVENTION

Embodiment modes of the present invention will be described below withreference to the drawings. It is easily understood by those skilled inthe art that the present invention can be carried out with variouschanges and modifications without departing from the content and thescope of the invention. Accordingly, the invention is to be interpretedwithout limitation to the descriptions in Embodiment Modes. Note that,in the drawings hereinafter referred to, the same reference numeralsdenote the same parts or parts having the same functions in differentdrawings, and the explanations will not be repeated.

Embodiment Mode 1

FIG. 1 is a cross-sectional view of an active matrix light emittingapparatus (a part of one pixel).

In FIG. 1, a TFT (p-channel TFT) provided over a substrate 10 having aninsulating surface controls current flowing to a second EL layer 20 bwhich emits light of blue, red, or green. Reference numerals 13 and 14denote a source region or a drain region. A glass substrate, a plasticsubstrate, or the like can be used as the substrate 10. Alternatively, asemiconductor substrate or a metal substrate which has an insulatingfilm on the surface can be used. A base insulating film 11 is formedover the substrate 10 (here, a bottom layer is a nitride insulating filmand a top layer is an oxide insulating film). A gate insulating film 12is provided between a gate electrode 15 and a semiconductor layer.Reference numeral 16 denotes an interlayer insulating film formed ofwith a single layer or a stack of an inorganic material, such as siliconoxide, silicon nitride, silicon nitride oxide, aluminum nitride, and/oraluminum nitride oxide. Although not shown, at least one or more TFTs(n-channel TFT or p-channel TFT) is/are additionally provided in onepixel. A TFT described here has one channel forming region; the numberof the channel forming region is not limited thereto and a plurality ofchannels may be provided.

Reference numerals 18 a to 18 d are equivalent to a first electrodewhich partially functions as an anode (or a cathode) of a light emittingelement. The first electrode has a structure in which a first regionhaving two layers, a second region having four layers, and a step iscaused at the boundary of the first region and the second region.

Here, reference numeral 18 a is a titanium film, 18 b is a titaniumnitride film, 18 c is a film mainly containing aluminum, and 18 d is atitanium nitride film. The films are stacked in order and the titaniumnitride film (a layer of the first electrode, denoted by 18 b) which isin contact with a buffer layer 20 a is used as an anode. A titaniumnitride is preferably used because good contact resistance with thebuffer layer 20 a can be obtained.

Further, a power supply line denoted by 17 a to 17 d is formed to havesimilar layered structure (four layers in total). The layered structure(four layers in total) includes a film mainly containing aluminum. Thus,a low resistance wiring can be formed, and a source wiring or the likecan be formed at the same time.

For example, in the case where the first electrode 18 a is a 60 nm thickTi film, the first electrode 18 b is a 100 nm thick TiN film, the firstelectrode 18 c is a 350 nm thick Al—Ti film, and the first electrode 18d is a 100 nm thick Ti film, a resist mask is formed to conduct etching.BCl₃ at 60 sccm and Cl₂ at 20 sccm are used as reactive gases, an RF(13.56 MHz) power of 450 W is applied to a coil shaped electrode at apressure of 1.9 Pa, an RF (13.56 MHz) power of 100 W is applied to asubstrate side (a sample stage), thereby conducting etching by using ICPetching apparatus. The region where Al—Ti (the first electrode 18 c) isetched is etched over for 15 seconds to expose TiN (the first electrode18 b).

After forming the first electrode having a step due to the etching, aninsulator 19 covering the step is formed. The insulator 19 is placed atthe boundary with an adjacent pixel to surround the periphery of thefirst electrode. The thickness of the insulator 19 is important forkeeping distance between an evaporation mask to be in contact with theinsulator 19 in a subsequent step and the first electrode. The thicknessof the insulator is desirably thick. In this embodiment mode, afour-layer wiring can be provided under the insulator 19; therefore,sufficient distance can be kept between the top surface of the insulator19 and the first electrode.

Reference numeral 21 denotes a second electrode formed with alight-transmitting conductive film which functions as a cathode (or ananode) of an organic light emitting element. As the light-transmittingconductive film, ITO (indium oxide-tin oxide alloy) film, an indiumoxide-zing oxide alloy (In₂O₃—ZnO), ZnO (zinc oxide), indium tin oxidecontaining silicon oxide (ITSO), tin oxide (SnO₂), or the like can beused. Further, the second electrode 21 is not particularly limited aslong as it is transparent to visible light. For example, a stack of athin metal layer (typically, an alloy such as MgAg, MgIn, or AlLi, or Agor Al) and a light-transmitting conductive film can be used.

In this specification, being transparent to visible light means having avisible light transmittance of 80% to 100%.

A stack containing an EL layer, namely, a stack containing an organiccompound (a stack of a first EL layer (buffer layer) 20 a and a secondEL layer 20 b) is provided between the first electrode and the secondelectrode. The buffer layer 20 a is a composite layer containing a metaloxide (such as molybdenum oxide, tungsten oxide, or rhenium oxide), anorganic compound (a material having hole transporting characteristics(for example,N,N′-bis(3-methylphenyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine(abbreviated to TPD), 4,4′-bis[N-(1-napthyl)-N-phenyl-amino]biphenyl(abbreviated to a-NPD) or4,4′-bis[N-[4-{N,N-bis(3-methylphenyl)amino}phenyl]-N-phenylamino]biphenyl(abbreviated to DNTPD)), or the like. The second EL layer 20 b may beformed using, for example, tris(8-quinolinolato) aluminum (abbreviatedas Alq₃), tris(4-methyl-8-quinolinolato) aluminum (abbreviated as Almq₃)or a-NPD. Alternatively, the second EL layer 20 b may be formed tocontain a dopant material such as N,N′-dimethyl quinacridone(abbreviated as DMQd), Coumarin 6 or rubrene. The stack containing anorganic compound, which is provided between the first electrode and thesecond electrode, may be formed by vapor deposition such as resistanceheating.

The thickness of the buffer layer 20 a is controlled so that thedistance between the first electrode and the second EL layer 20 b iscontrolled, thereby improving the light emission efficiency. Bycontrolling the thickness of the buffer layer, an excellent image can bedisplayed with clear color light emitted from each light emittingelement; thus, a light emitting device with low power consumption can berealized.

Alternatively, an auxiliary wiring may be provided on the secondelectrode 21 so as to lower the resistance of the second electrode 21.

Although not shown, a protective film is preferably formed over thesecond electrode 21 in order to improve the reliability of the lightemitting device. This protective film is an insulating film which mainlycontains silicon nitride or silicon nitride oxide, which is formed bysputtering (a DC method or an RF method), or a thin film which mainlycontains carbon.

Further, a top gate TFT is described as an example here; however, theinvention is applicable, regardless of the TFT structure, for example,to a bottom gate (inverted staggered) TFT or a staggered TFT. Further,the structure of the TFT is not limited to a single gate structure, andthe TFT may have a multi-gate structure including a plurality of channelforming regions, for example, a double-gate structure.

In this specification, a semiconductor film mainly containing silicon, asemiconductor film mainly containing an organic material, or asemiconductor film mainly containing a metal oxide can be used as asemiconductor layer serving as an active layer of a TFT. As asemiconductor film mainly containing silicon, an amorphous semiconductorfilm, a semiconductor film having a crystalline structure, a compoundsemiconductor film having an amorphous structure, or the like can beused. Specifically, an amorphous silicon, microcrystalline silicon,polycrystalline silicon, or the like can be used. As a semiconductorfilm mainly containing an organic material, a semiconductor film mainlycontaining a substance which includes a certain amount of carbon or anallotrope of carbon (excluding diamond), which is combined with anotherelement, can be used. Specifically, pentacene, tetracene, a thiophenoligomer derivative, a phenylene derivative, a phthalocyanine compound,a polyacetylene derivative, a polythiophene derivative, a cyanine dye,or the like can be used. Further, as the semiconductor film mainlycontaining a metal oxide, zinc oxide (ZnO); an oxide of zinc, gallium,and indium (In—Ga—Zn—O); or the like can be used.

An example of the pixel structure of a light emitting device is shown inFIG. 2A. FIG. 2B shows a cross-sectional view taken along chain lineA-A′ in FIG. 2A. An example of steps for manufacturing a light emittingdevice will be described with reference to the drawings.

First, a base insulating film 31 is formed over a substrate 30 which hasan insulating surface.

A silicon oxynitride film is formed as the first layer of the baseinsulating film 31 to a thickness of 10 nm to 200 nm (preferably, 50 nmto 100 nm) by plasma CVD using a reactive gas of SiH₄, NH₃, and N₂O.Here, a silicon oxynitride film (composition ratio: Si=32%, O=27%,N=24%, H=17%) is formed to a thickness of 50 nm. A silicon oxynitridefilm is formed thereover as the second layer of the base insulating filmto a thickness of 50 nm to 200 nm (preferably, 100 nm to 150 nm) byplasma CVD using a reactive gas of SiH₄ and N₂O. Here, a siliconoxynitride film (composition ratio: Si=32%, O=59%, N=7%, H=2%) is formedto a thickness of 100 nm. The base insulating film 31 in this embodimentmode has two layers. Alternatively, the base insulating film 31 may havea single layer or a stack including three or more layers.

A semiconductor layer is formed over the base insulating film. Thesemiconductor layer to be an active layer of a TFT is formed as follows:an amorphous semiconductor film is formed by a known means (sputtering,LPCVD, plasma CVD, or the like); the film is crystallized by a knowncrystallization method (a laser crystallization method, a thermalcrystallization method, or a thermal crystallization method using acatalyst such as nickel); and the crystalline semiconductor film ispatterned into a desired shape. The thickness of the semiconductor layeris 25 nm to 80 nm (preferably, 30 nm to 60 nm). The material of thecrystalline semiconductor film is not particularly limited; however,silicon or a silicon-germanium alloy is preferably used.

In the case of forming a crystalline semiconductor film by a lasercrystallization method, an excimer laser, a YAG laser, or an YVO₄ laserwhich emits a pulsed or continuous-wave light can be used. In the caseof using such a laser, the semiconductor film is preferably irradiatedwith laser light from a laser oscillator, which is condensed in a linearshape by an optical system. The conditions of crystallization areappropriately selected by the practitioner of the invention. In the caseof using an excimer laser, the pulse repetition rate is 30 Hz and thelaser energy density is 100 mJ/cm² to 400 mJ/cm² (typically, 200 mJ/cm²to 300 mJ/cm²). Meanwhile, in the case of using a YAG laser, the secondharmonic is preferably used; the pulse repetition rate is 1 kHz to 10kHz, and laser energy density is 300 mJ/cm² to 600 mJ/cm² (typically,350 mJ/cm² to 500 mJ/cm²). The laser light condensed into a linear shapewith a width of from 100 μm to 1000 μm, for example, 400 μm, is emittedthroughout the substrate surface. The overlap ratio of the linear laserlight at that time is preferably 80% to 98%.

A fundamental wave may be used without having laser light pass through anon-linear optical element, and laser annealing is conducted byirradiating an amorphous semiconductor film with pulsed laser lighthaving high intensity and high repetition rate, thereby forming acrystalline semiconductor film. High intensity means a high peak outputpower per unit of time and area, and the peak output power of the laserlight ranges from 1 GW/cm² to 1 TW/cm². A fundamental wave with awavelength of about 1 μm is hardly absorbed so much by a semiconductorthin film in irradiating the semiconductor thin film with thefundamental wave. Thus, the fundamental wave has a low absorptionefficiency. However, a fundamental wave emitted from a pulsed laserhaving a pulse width in the range of picoseconds, or in the range offemtoseconds (10⁻¹⁵ seconds) can provide high intensity laser light.Thus, a non-linear optical effect (multiphoton absorption) is caused andthe fundamental wave is absorbed by the semiconductor film. Since anon-linear optical element is not used and thus light is not convertedto a harmonic, a laser oscillator having a higher output power than 15W, for example, 40 W, can be used for laser annealing. Therefore, thewidth of a region having large grain crystals that is formed by scanningonce can be increased, and thus the productivity can be improvedsignificantly.

Subsequently, the surface of the semiconductor layer is cleaned with anetchant containing hydrogen fluoride, and a gate insulating film 33covering the semiconductor layer is formed. The gate insulating film 33is formed by depositing an insulating film containing silicon to have athickness of 40 to 150 nm by plasma CVD or sputtering. In thisembodiment mode, a silicon oxide nitride film is deposited (compositionratio: Si=32%, O=59%, N=7% and H=2%) to a thickness of 115 nm by plasmaCVD. Naturally, the gate insulating film is not limited to a siliconoxide nitride film but may be formed with another insulating filmcontaining silicon, which has a single layer or a layered structure.

After cleaning the surface of the gate insulating film 33, a gateelectrode is formed.

Then, an impurity element imparting p-type conductivity (such as B),appropriate amount of boron here, is added to the semiconductor to forma source/drain region 32. After the addition of the impurity element,heat treatment, irradiation with intense light, or irradiation withlaser light is carried out in order to activate the impurity element.Concurrently with the activation, plasma damage to the gate insulatingfilm or to the boundary face between the gate insulating film and thesemiconductor layer can be repaired. It is extremely effective toirradiate the main or the back surface with the second harmonic of a YAGlaser to activate the impurity element particularly in the atmosphere ofroom temperature to 300° C. A YAG laser is a preferable activating meansbecause it requires a few maintenances.

The subsequent processes are carried out as follows: an interlayerinsulating film 35 is formed of an organic or inorganic material(including a deposited silicon oxide film, PSG (glass doped withphosphorus), BPSG (glass doped with boron and phosphorus), or the like),the semiconductor layer is hydrogenated, and contact holes reaching thesource/drain regions are formed. Then, a source electrode (wiring 34)and a first electrode (drain electrode) 36 a to 36 d are formed, and theTFT (p-channel TFT) is completed.

Although a p-channel TFT is described this embodiment mode, an n-typeimpurity element (such as P or As) can be used instead of a p-typeimpurity element to form the n-channel TFT.

The first electrode (layers 36 a to 36 d) and the wiring 34 are formedwith a film mainly including an element selected from Ti, TiN, TiSiXNY,Al, Ag, Ni, W, WSiX, WNX, WSiXNY, Ta, TaNX, TaSiXNY, NbN, MoN, Cr, Pt,Zn, Sn, In, or Mo; an alloy material or a compound material containingthe above element, or a stack thereof with a total thickness range of100 nm to 800 nm.

Particularly, in the first layer 36 a which is in contact with the drainregion 32, is preferably formed of Ti that can make an ohmic contactwith silicon to a thickness of 10 nm to 100 nm. The second layer 36 b ofthe first electrode is preferably formed of a material having a highwork function in the case where the film is thin (TiN, TaN, MoN, Pt, Cr,W, Ni, Zn, Sn) to a thickness of 10 nm to 100 nm. The second layer 36 balso functions as a blocking layer for preventing the third layer 36 cand the first layer 36 a of the first electrode from being alloyed witheach other. As the material for forming the fourth layer 36 d, amaterial which can prevent oxidization, corrosion, and hillocks of thethird layer 36 c is preferably used; a metal nitride (TiN, WN, or thelike) is preferable and the thickness may be in the range of 20 nm to100 nm.

Next, a resist mask is formed, and the first electrode is processed byetching as in the structure shown in FIG. 2B. FIG. 2A shows a boundarybetween the first region and the second region, that is, the contour ofthe third layer 36 c.

After the resist mask is removed, an insulator 37 covering the step ofthe first electrode is formed. The contour of the insulator 37 is shownin FIG. 2A.

Next, a stack of layers 38 a and 38 b which contains an organic compoundis formed by vapor deposition. Then, a second electrode 39 is formed.

The thus obtained light emitting element emits light in the directionindicated by the arrow in FIG. 2B.

After the second electrode (conductive film 39) is formed, the lightemitting element formed over the substrate 30 is sealed by attaching asealing substrate (transparent substrate) to the substrate using asealing material or a sheet adhesive material. Spacers formed from aresin film may be provided in order to keep the gap between the sealingsubstrate and the light emitting element. The space surrounded by thesealing material is filled with nitrogen or other inert gas. For thesealing material, an epoxy resin is preferably used. Desirably, thematerial of the sealing material transmits as little moisture and oxygenas possible. A substance having an effect of absorbing oxygen andmoisture (a desiccant or the like) may be placed in the space surroundedby the sealing material.

By enclosing the light emitting element in a space as above, the lightemitting element can be completely shut off from the outside andsubstances that accelerate degradation of the organic compound layer,such as moisture and oxygen, can be prevented from entering the lightemitting element from the outside. Accordingly, a highly reliable lightemitting device can be obtained.

Embodiment Mode 2

FIG. 3 shows an example of a structure according to this embodiment modewhich is different from the one in Embodiment Mode 1. FIG. 3 shows astructure in which a first electrode is not directly in contact with asemiconductor layer of a TFT, but is electrically connected to thesemiconductor layer of the TFT through another electrode. The firstelectrode has a structure in which a first region formed with a singlemetal layer and a second region having three layers are provided, and astep is caused between the first region and the second region. In orderto improve the aperture ratio, the first region is provided at only theperiphery of the contact hole, and the second region is provided in allthe other regions.

In this embodiment mode, an example of forming a pixel area and a drivercircuit over one substrate will be described.

First, as in Embodiment Mode 1, a base insulating film 311, asemiconductor layer formed with a crystalline semiconductor film, and agate insulating film 312 are formed over a substrate 310 having aninsulating surface.

Next, an electrode 315 to be a gate electrode of a TFT of a pixel areaand electrodes 338 and 337 which are to be a gate electrode of a TFT ofa driver circuit are formed. Subsequently, an impurity element (such asB) which imparts p-type conductivity to a semiconductor, boron here, isselectively added using a resist mask, to form p-type high concentrationimpurity regions 313, 314, 331, and 332. After removing the resist mask,another resist mask is formed to form a low concentration impurityregion by selectively adding an impurity element which imparts n-typeconductivity (such as P or As), phosphorous here, thereby forming an LDDregion. Further, after removing the resist mask, still another resistmask is formed, and phosphorous is selectively added to thesemiconductor layer to form high concentration level impurity regions333 and 334 are formed. Note that, the low concentration impurity regionto which phosphorous is added only once becomes LDD regions 335 and 336.

The order of the dopings is not limited in particular.

After removing the resist mask, heat treatment, irradiation with intenselight, or irradiation with laser light is carried out in order toactivate the impurity element.

Next, a first interlayer insulating film 316 formed of an organicmaterial or an inorganic material is formed, and hydrogenation iscarried out. Subsequently, contact holes which reach the highconcentration impurity region is formed in a first interlayer insulatingfilm 316 and a gate insulating film. Next, electrodes 317, 318, and 341to 344 to be source/drain electrodes to form a plurality of kinds ofTFTs (p-channel TFT and n-channel TFT).

A p-channel TFT having an electrode 315 as a gate electrode is formed inthe pixel area. An n-channel TFT having an electrode 338 as a gateelectrode and a p-channel TFT having an electrode 337 as a gateelectrode are formed in the driver circuit area. Note that, then-channel TFT in the driver circuit area includes a channel formingregion 340, and the p-channel TFT in the driver circuit area includes achannel forming region 339.

Next, a second interlayer insulating film 309 formed of an organicmaterial or an inorganic material is formed. Subsequently, contact holeswhich reach electrodes 318, 342, and 343 are formed in the secondinterlayer insulating film 309.

A metal film having three layers is formed over the second interlayerinsulating film 309. The three layer metal film may be a stack of filmseach of which mainly includes an element selected from Ti, TiN, TiSiXNY,Al, Ag, Ni, W, WSiX, WNX, WSiXNY, Ta, TaNX, TaSiXNY, NbN, MoN, Cr, Pt,Zn, Sn, In, or Mo; an alloy material or a compound material containingthe above element with a total thickness range of 100 nm to 800 nm.

Here, three layers of a Ti film, an Al film, and a Ti film are stackedin order.

Next, a resist mask is formed and etching is carried out to formconnection electrodes 345 a to 345 c and a first electrode. A leadwiring having a similar layered structure can also be formed at the sametime as the connection electrodes; therefore, the area occupied by thedriver circuit area can be reduced.

After removing the resist mask, another resist mask is formed toselectively etch the first electrode. Thus, the first electrode has astructure in which a first region formed with only a first layer 308 a,and a second region formed with three layers in total including thefirst layer 308 a, a second layer 308 b, and a third layer 308 c areprovided, and a step is caused between the first region and the secondregion.

After the resist mask is removed, an insulator 319 covering the step ofthe first electrode is formed.

Next, a stack having layers 320 a and 320 b containing an organiccompound is formed by vapor deposition. The layer 320 a is a bufferlayer which is a composite layer containing a metal oxide (such asmolybdenum oxide, tungsten oxide, or rhenium oxide), an organic compound(a material having hole transporting characteristics (for example,N,N′-bis(3-methylphenyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine(abbreviated to TPD), 4,4′-bis[N-(1-napthyl)-N-phenyl-amino]biphenyl(abbreviated to α-NPD) or4,4′-bis[N-[4-{N,N-bis(3-methylphenyl)amino}phenyl]-N-phenylamino]biphenyl(abbreviated to DNTPD)), or the like. The layer 320 b is a single layeror a stack which includes a light emitting layer. The thickness of thebuffer layer 320 a is controlled so that the distance between the firstelectrode and the second light emitting layer is controlled, therebyimproving the light emission efficiency.

Next, a second electrode 321 is formed. Ag, Al; an alloy such as MgAg,MgIn, AlLi; or a light-transmitting film which is formed by codepositionof aluminum and an element in group 1 or group 2 of the periodic tablecan be used for the second electrode 321. Here, a top emission lightemitting device which emits light through the second electrode ismanufactured here; thus, a thin metal layer having a thickness of about1 nm to 20 nm is used as the second electrode. The second electrode 321may be thin enough to transmit light.

In addition, a transparent conductive film may be stacked over thesecond electrode 321.

The thus obtained light emitting element (also referred to as an ELelement) emits light in the direction indicated by the arrow in FIG. 3.

After the second electrode 321 is formed, the light emitting elementformed over the substrate 310 is sealed by attaching a sealing substrate(transparent substrate) to the substrate using a sealing material or asheet adhesive material. The sealing substrate is preferably attached inan atmosphere containing an inert gas (rare gas or nitrogen).

Next, an unnecessary part of the substrate is cut off. In the case ofobtaining a plurality of panels from one substrate, each panel isseparated off. In the case of obtaining one panel from one substrate,the cutting step can be omitted by pasting a counter substrate which iscut in advance. At this stage, an EL module is completed.

The whole EL module will be described with reference to FIGS. 4A and 4B.FIG. 4A is a top view of an EL module, and FIG. 4B is a cross-sectionalview of a part thereof.

A substrate provided with many TFTs (also referred to as a TFTsubstrate) is further provided with a pixel area 40 where display isperformed, driver circuit areas 41 a and 41 b for driving each pixel inthe pixel area, a connection portion 43 where a second electrode formedover an EL layer is connected with a lead wiring, and a terminal area 42to which an FPC is attached for connecting to an external circuit.

The EL element is sealed with a sealing substrate 48 for sealing an ELelement, a sheet adhesive material 44, and a sealing material 49. FIG.4B is a cross-sectional view taken along chain line A-A′ in FIG. 4A.

Innumeral pixels are regularly arranged on the pixel area 40. Althoughnot shown here, the pixels are arranged in stripe arrangement in an Xdirection, for example, in the order of R, G, and B. Further, thearrangement of light emitting elements is not limited; for example,delta arrangement, mosaic arrangement, or the like may be used.

As shown in FIG. 4B, a gap holding member 50 is provided so that aspacing of about 2 μm to 30 μm is kept between the pair of thesubstrates. Further, the sealing substrate 48 is attached with thesealing material 49; thus, all light emitting elements are sealed. Notethat, if the light emitting elements can be sufficiently sealed withonly the sheet adhesive material 44, the sealing material 49 is notrequired in particular. Further, if sufficient space can be kept betweenthe pair of the substrates with only the sheet adhesive material 44, thegap holding member 50 is not particularly required to be provided.

A depressed portion may be formed on a part of the sealing substrate 48,which is not overlapped with the pixel area by a sandblast method. Adesiccant may be provided in the depressed portion.

In this embodiment mode, a lead wiring having a similar layeredstructure can also be formed at the same time as the connectionelectrodes 345 a to 345 c; therefore, the area occupied by the drivercircuit area can be reduced and the peripheral circuit area around thepixel area can be reduced. Further, a terminal electrode of the terminalarea 42 may be formed to have a layered structure similar to theconnection electrodes 345 a to 345 c.

Note that, this embodiment mode can be freely combined with EmbodimentMode 1.

Embodiment Mode 3

Here, several methods for manufacturing a full-color display device willbe described. Specifically, a method in which three light emittingelements are used; a method in which a white light emitting element anda color filter are used in combination; a method in which a blue lightemitting element and a color conversion layer are used in combination; amethod in which a white light emitting element, a color conversionlayer, and a color filter are used in combination; or the like may beused.

In the case of using three light emitting elements for performing fullcolor display, pixels each of which is provided with a red lightemitting element, a blue light emitting element, and a green lightemitting element, which are regularly arranged are arranged in a pixelarea. For example, three kinds of evaporation masks having differentopening positions for each light emission colors of R, G, and B, therebyproviding light emitting layers of R, G, and B by vapor deposition.

By controlling the thickness of the buffer layer for each light emittinglayer, which is deposited before forming the light emitting layers, anexcellent image can be displayed with clear color light emitted fromeach light emitting element. Thus, a light emitting device with lowpower consumption can be realized.

The arrangement, including a stripe pattern which is simplest, such asdiagonal mosaic arrangement, triangle mosaic arrangement, RGBG fourpixel arrangement, RGBW four pixel arrangement, or the like can be usedfor the arrangement of the light emitting elements (R, G, and B).

In addition, the color purity may be improved by using a color filter incombination.

A coloring layer for the emission color of the light emitting elementmay be provided to overlap the light emitting element. For example, ablue coloring layer may be provided to overlap a blue light emittingelement.

A method in which a white color emitting element and a color filter areused in combination (hereinafter, referred to as a color filter method)will be explained below with reference to FIG. 5A.

The color filter method is a method in which a light emitting elementhaving a layer containing an organic compound, which emits white lightis formed and the obtained white light is made pass through a colorfilter to obtain light of red, green, and blue.

Although there are various methods of obtaining white color light, thecase of using a light emitting layer containing a high molecular weightmaterial which can be formed by coating will be explained here. In thiscase, doping with a color pigment to the high molecular weight materialfor forming a light emitting layer can be carried out by preparing asolution and can be much more easily achieved in comparison with a vapordeposition method for carrying out co-evaporation for doping a pluralityof pigments.

Specifically, after an aqueous solution ofpoly(ethylenedioxythiophene)/poly(stylenesulfonic acid) (PEDOT/PSS)which functions as a hole injecting layer is applied over the entiresurface of an anode containing a metal having large work function (Pt,Cr, W, Ni, Zn, Sn, In) by coating and baked, a polyvinyl carbazole (PVK)solution doped with a luminescence center pigment (1,1,4,4-tetraphenyl1,3-butadience (TPB),4-dicyanomethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM1),Nile red, coumarin 6, or the like) is applied over the entire surface bycoating and baked as the light emitting layer, a cathode having a stackof a thin film including metal having small work function (Li, Mg, Cs)and a transparent conductive film (ITO (indium oxide tin oxide alloy),indium oxide zinc oxide alloy (In₂O₃—ZnO), zinc oxide (ZnO) or the like)stacked thereover is thereafter formed. PEDOT/PSS uses water as asolvent and is not dissolved in an organic solvent. Therefore, even whenPVK is applied thereonto by coating, there is no concern ofredissolving. Further, since different kinds of solvents are used forPEDOT/PSS and PVK, it is preferable that different film forming chambersare used therefor.

Further, although an example of using a stack of compound layers isshown in the above-described example, a single layer of an organiccompound containing layer can be used. For example, PBD having electrontransporting characteristics may be dispersed in polyvinyl carbazole(PVK) having hole transporting characteristics. Further, white colorlight can be obtained by dispersing 30 wt % of PBD as an electrontransporting agent and dispersing pertinent amounts of four kinds ofcolor pigments (TPB, coumarin 6, DCM1, and Nile red).

Further, the layer containing the organic compound layer is formedbetween the anode and the cathode; holes injected from the anode andelectrons injected from the cathode are combined at the layer containingthe organic compound layer; thus, white color light can be obtained inthe layer containing the organic compound layer.

Alternatively, it is also possible to obtain white color light as awhole by appropriately selecting an organic compound layer which emitsred color light, an organic compound layer which emits green colorlight, and an organic compound layer which emits blue color light, whichare overlap to be mixed.

The organic compound films formed as described above can provide whitecolor light as a whole.

Color filters respectively provided with the coloring layer (R) whichabsorbs light except for red color light, a coloring layer (G) whichabsorbing light except for green color luminescence and the coloringlayer (B) which absorbs light except for blue light are formed in adirection of white color light emission from the organic compound layer;thus, white color light, white color luminescence from the lightemitting elements can respectively be separated to obtain red colorlight, green color light, and blue color light. Further, in the case ofan active matrix light emitting device, a structure in which TFTs areformed between the substrate and the color filter is used.

The arrangement, including a stripe pattern which is simplest, such asdiagonal mosaic arrangement, triangle mosaic arrangement, RGBG fourpixel arrangement, RGBW four pixel arrangement, or the like can be usedfor the arrangement of the coloring layers (R, G, and B).

A coloring layer for constituting a color filter is formed using a colorresist containing an organic photosensitive material in which a pigmentis dispersed. Color reproducibility as full color is sufficientlyensured by combining white luminescence and a color filter.

Further, in this case, even when different colors of light is to beobtained, since all the organic compound films emit white color light,it is not necessary to form the organic compound films to have differentcharacteristics depending on the light emission colors. Further, acircularly polarizing plate for preventing mirror reflection is notparticularly needed.

Next, a CCM (color changing mediums) method realized by combining a bluecolor light emitting element having a blue color luminescent organiccompound film and a fluorescent color conversion layer will be explainedwith reference to FIG. 5B.

According to the CCM method, the fluorescent color conversion layer isexcited by blue color light emitted from the blue color emitting elementand the color is changed using each color conversion layer.Specifically, changing from blue color to red color using the colorconversion layer (B→R), changing from blue color to green color usingthe color conversion layer (B→G) and changing from blue color to purerblue color using the color conversion layer (B→B) (further, changingfrom blue color to blue color is not necessarily carried out) arecarried out to obtain red color, green color and blue color light. Alsoin the case of the CCM method, the structure in which TFTs are formedbetween the substrate and the color conversion layer is used in the caseof an active matrix light emitting device.

Also in this case, it is not necessary to form the organic compoundfilms to have different characteristics depending on the light emissioncolors. Further, a circularly polarizing plate for preventing mirrorreflection is not particularly needed.

Further, when the CCM method is used, since the color conversion layeris fluorescent, the color conversion layer is excited by external light,which causes a problem of reduction in contrast. Therefore, as shown byFIG. 5C, the contrast may be made improved by providing color filters.

Further, this embodiment mode can be freely combined with EmbodimentModes 1 and 2.

Embodiment Mode 4

FIG. 6 shows an example of a multi-chamber manufacturing apparatus, inwhich a multi-chamber for depositing a layer containing an organiccompound or the like, and a chamber for sealing are provided as oneunit. Only one unit is used, thereby preventing impurities such asmoisture from mixing or improving the throughput.

The manufacturing apparatus shown in FIG. 6 includes transport chambers102, 104 a, 108, 114, and 118, delivery chambers 101, 105, 107, and 111,a first film formation chamber 106E, a second film formation chamber106B, a third film formation chamber 106G, a fourth film formationchamber 106R, a fifth film formation chamber 106F, other film formationchambers 109, 110, 112, 113, and 132, a baking chamber 123, a mask stockchamber 124, substrate stock chambers 130 a and 130 b, a substrateloading chamber 120, and a multi-stage vacuum heating chamber 103. Notethat, the transport chamber 104 a is provided with a transportingmechanism for transporting a substrate, and the other transport chambersare each provided with the same transporting mechanism.

In addition, the manufacturing apparatus shown in FIG. 6 includes, anunloading chamber 119, a delivery chamber 141, a hardening treatmentchamber 143, an attachment chamber 144, a seal formation chamber 145, apretreatment chamber 146, and a sealing substrate loading chamber 117.Incidentally, gates are provided between the chambers.

A procedure for carrying a substrate, on which an anode (firstelectrode) and an insulator (partition wall) covering an end of theanode are provided in advance, into a manufacturing apparatus shown inFIG. 6 to manufacture a light emitting device will be hereinafterdescribed.

A thin film transistor connected to the anode (TFT for current control)and a plurality of other thin film transistors (TFT for switching, orthe like) are provided on a substrate in advance

First, the substrate (600 mm×720 mm) is set in a substrate loadingchamber 120. Such a large substrate having a size of 320 mm×400 mm, 370mm×470 mm, 550 mm×650 mm, 600 mm×720 mm, 680 mm×880 mm, 1000 mm×1200 mm,1100 mm×1250 mm, or 1150 mm×1300 mm can be used.

The substrate (provided with an anode and an insulator covering an endof the anode) set in the substrate loading chamber 120 is transferred toa transport chamber 118 in which the atmospheric pressure is kept. Notethat a transport mechanism (transport robot or the like) fortransferring and reversing the substrate is provided in the transportchamber 118.

Transport chambers 108, 114, and 102 are each provided with a transportmechanism and an evacuation means. The robot provided in the transportchamber 118 can reverse the front and the back of the substrate and cancarry the substrate into a delivery chamber 101 in a reversed state. Thedelivery chamber 101 is connected to an evacuation treatment chamber andcan be made vacuum by being evacuated and can be pressurized to theatmospheric pressure by introducing an inert gas after being theevacuation.

The evacuation treatment chamber is provided with a turbomolecular pumpof a magnetically levitated type, a cryopump, or a dry pump. Thus, thetransport chambers connected to respective chambers can be evacuated to10⁻⁵ Pa to 10⁻⁶ Pa. Moreover, back diffusion of impurities from the pumpside and an exhaust system can be controlled.

Subsequently, the substrate is transferred from the transport chamber118 to the delivery chamber 101 and is further transferred from thedelivery chamber 101 to the transport chamber 102 without exposure tothe atmosphere.

In addition, in order to eliminate shrinkage, it is preferable toperform vacuum heating before the evaporation of a film containing anorganic compound. In order to transfer the substrate from the transportchamber 102 to a multi-stage vacuum heating chamber 103 and thoroughlyremove moisture and the other gases contained in the substrate,annealing for degasification is performed in vacuum (5×10⁻³ Torr (0.665Pa) or less, preferably 10⁻⁴ Pa to 10⁻⁶ Pa). In the multi-stage vacuumheating chamber 103, a plurality of substrates is heated uniformly usinga flat heater (typically, a sheath heater). A plurality of the flatheaters is set, and the substrates can be heated from both sides as thesubstrates are sandwiched in the flat heaters. Naturally, the substratescan be heated from one side. In particular, in the case in which anorganic resin film is used as a material for the interlayer insulatingfilm or the partition wall, since the organic resin film may absorbmoisture and degasification may occur, it is effective to perform vacuumheating, in which the substrates are heated at 100° C. to 250° C.,preferably, 150° C. to 200° C., for example, for thirty minutes or moreand thereafter cooled naturally for thirty minutes, before forming thelayer containing an organic compound to remove adsorbed moisture or thelike.

If necessary, a hole injection layer containing a high molecular weightmaterial may be formed in the film formation chamber 112 by an ink jetmethod, spin coating, a spraying method, or the like. After forming thehole injection layer by a coating method, it is preferable to performheating under the atmospheric pressure or vacuum heating (at 100° C. to200° C.) in the baking chamber 123 immediately before the film formationby a deposition method.

In addition, in the case in where a film of PEDOT/PSS is formed by spincoating, since the film is formed on the entire surface, the film on anend face or the periphery of the substrate, a terminal portion, aconnection area between a cathode and a lower wiring, and the like arepreferably removed in a selective manner, and it is preferable to removethe film by O₂ ashing or the like using a mask in a selective manner ina pretreatment chamber connected to the transport chamber 102.

In this embodiment mode, a substrate is transferred from the transportchamber 102 to the film formation chamber 106F to deposit a buffer layeron the first electrode.

An example of depositing a buffer layer will be shown. First,4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviated to NPB) andmolybdenum oxide are stored in separate evaporation sources ofresistance heating type, and they are deposited onto a substrate havinga first electrode, which is set inside an evacuated depositionapparatus. In the vapor deposition, NPB is deposited at a depositionrate of 0.4 nm/s while molybdenum oxide is evaporated at an amount of1/4 (weight ratio) relatively to NPB. In this case, in terms of a molarratio, NPB:molybdenum oxide is 1:1. The first composite layer containinga metal oxide and an organic compound has a thickness of 50 nm.

FIG. 7A shows a perspective view of an example of a deposition apparatusof the film formation chamber 106F. The mechanism of the depositionapparatus will be briefly described below.

The substrate 701 is aligned with an evaporation mask 702 in advance.The substrate is transported in a substrate transport direction 706 a(direction indicated by the arrow in FIG. 7A) in the aligned state. Thesubstrate is transported using a substrate transport means (transportrobot or transport roller) so that the substrate passes over andeposition shield 703 a. The deposition shield 703 a has an opening 703b so that the deposition material from an evaporation source 704 issublimated through the opening. The deposition shield 703 a is heated sothat the deposition material does not adhere to the deposition shielditself thereby keeping a sublimation direction 706 b of the depositionmaterial. A heater is provided in contact with the deposition shield. Aheating temperature may be controlled by a computer connected to theheater.

The evaporation source 704 has a structure on which a plurality ofcrucibles can be provided. The evaporation source 704 can be moved in adirection indicated by an arrow 705. An evaporation direction may bechanged by changing a direction of the evaporation source 704 instead ofmoving the evaporation source. Resistance heating is used for thedeposition method. Further, the range of the movement of the evaporationsource is desirably larger than the width of the substrate Wa so thatthe uniformity of the thickness of the deposited film is improved.Further, the width of the adhesive shield Wb is also preferably longerthan the substrate width Wa, so that the uniformity of the filmthickness of the deposited film is improved.

In the case where the evaporation source is fixed when the deposition isconducted, the deposition material spreads concentrically over thesubstrate; thus, there is a fear that the thickness of the part whichoverlaps the evaporation source, that is, the thickness of the centerpart which spreads concentrically becomes thick. In the invention, thedeposition material is prevented from spreading concentrically by theadhesive shield, and the evaporation source is moved; thus, theuniformity of the thickness is improved significantly.

Note that, in a deposition apparatus shown in FIG. 7A, the opening inthe adhesive shield has an elongated elliptical shape; however, theshape and the number of the opening 703 b are not limited in particular.The opening has an elongated elliptical shape so that the depositionmaterial is prevented from stopping the opening.

In order to supply a deposition material to a plurality of crucibles inthe evaporation source, a setting chamber is provided which connects tothe film formation chamber through a gate. The evaporation sourceprovides a heater for heating the crucibles. The setting chamber ispreferably provided on a line extending in the moving direction of theevaporation source in the film formation chamber. After the depositionmaterial is supplied in the setting chamber, the setting chamber isevacuated to the same level as the film formation chamber, and heatingis conducted to a stable deposition rate using a film thickness monitorprovided in the setting chamber. Then, the gate is opened and theevaporation source is moved in one direction from the setting chamber tothe film formation chamber. The evaporation source is also moved in thefilm formation chamber while keeping the direction; so that thedeposition material is deposited on the substrate. The setting chamberis thus disposed so that the evaporation source can be moved smoothly.Further, a plurality of evaporation sources and adhesive shields may beprovided in one film formation chamber. FIG. 7B shows a top-view of adeposition apparatus in which a plurality of evaporation sources and asetting chambers are provided. A setting chamber 707 is provided in adirection 705 of the movement of the evaporation source. The depositionmaterial may supplied by moving the evaporation source to the settingchamber. In the case where the evaporation source is fixed in the filmformation chamber, the deposition material is supplied to theevaporation source necessarily at an atmospheric pressure in the filmformation chamber. Therefore, time is required for evacuating the filmformation chamber for redeposition. When the setting chamber 707 isprovided, atmospheric pressure and vacuum can be switched only in thesetting chamber 707 while the vacuum is kept in the film formationchamber 700; thus, the deposition material can be supplied in a shorttime.

Further, a second adhesive shield 709 is provided in parallel to theadhesive shield 703 a, and a second evaporation source 708 which movesin a direction perpendicular to the transfer direction of the substratemay be provided. A plurality of evaporation sources are provided in onefilm formation chamber; thus, sequential film formation into a stack canbe carried out. Here, an example of providing two evaporation sources inone film formation chamber is shown; however, more than two evaporationsources may be provided in one film formation chamber.

Next, the substrate is transferred to the delivery chamber 105 from thetransport chamber 102; then, the substrate can be transferred to thetransport chamber 104 a from the delivery chamber 105 without exposureto the atmosphere.

Next, the substrate is transferred to the film formation chambers 106R,106G, 106B, and 106E which are connected to the transport chamber 104 aas appropriate; thus, layers each containing an organic compound of lowmolecular weight molecules which are to be a red light emitting layer, agreen light emitting layer, a blue light emitting layer, and an electrontransport layer (or an electron injection layer) are formed asappropriate.

At least one of the film formation chambers 106R, 106G, 106B, and 106Eis a deposition apparatus shown in FIGS. 7A and 7B.

In the film formation chamber 106B, PPD(4,4′-bis(N-(9-phenanthryl)-N-phenylamino)biphenyl) doped with CBP(4,4′-bis(N-carbazolyl)-biphenyl) is deposited, using an evaporationmask, to a thickness of 30 nm as a blue light emitting layer in a regionto form a blue light emitting element.

In the film formation chamber 106R, Alq₃ doped with DCM is deposited,using an evaporation mask, to a thickness of 40 nm as a red lightemitting layer in a region to form a red light emitting element.

In the film formation chamber 106G, Alq₃ doped with DMQd is deposited,using an evaporation mask, to a thickness of 40 nm as a green lightemitting layer in a region to form a green light emitting element.

By suitably selecting an EL material and using a mask, a light emittingelement which can emit light of three colors (specifically, R, G, and B)as a whole can be formed.

An evaporation mask is stocked in mask stock chambers 124 andtransferred to film formation chambers as appropriated when vapordeposition is performed. Since the area of the mask is increased when alarge substrate is used, the size of a frame for fixing the mask isincreased, so that it is difficult to stock many masks. Thus, the twomask stock chambers 124 are prepared here. Cleaning of the evaporationmask may be performed in the mask stock chambers 124. In addition, sincethe mask stock chambers become empty at the time of vapor deposition, itis possible to stock a substrate in the mask stock chambers after filmformation or after treatment.

Subsequently, the substrate is transferred from the transport chamber104 a to a delivery chamber 107 and further transferred from thedelivery chamber 107 to the transport chamber 108 without exposure tothe atmosphere.

Subsequently, the substrate is transferred to a film formation chamber110 by a transport mechanism set in the transport chamber 108 to form acathode. This cathode is preferably transparent or translucent. It ispreferable to use a thin film (1 nm to 20 nm) of a metal film (alloysuch as MgAg, MgIn, LiF, or, a film formed of an element belonging tothe first group or second group in a periodic table and aluminum by acodeposition, or a stack of these films) formed by vapor depositionusing resistance heating or a stack of the thin film (1 nm to 10 nm) ofthe metal film and a transparent conductive film as a cathode. In thecase of using a stack, the substrate is transferred to a film formationchamber 109, and a transparent conductive film is formed by sputtering.

A light emitting element having a layered structure including theorganic compound layer is formed through the above process.

In addition, the substrate may be transferred to a film formationchamber 113 connected to the transport chamber 108 and sealed by forminga protective film consisting of a silicon nitride film or a siliconnitride oxide film. Here, a target of silicon, a target of siliconoxide, or a target of silicon nitride is provided in the film formationchamber 113.

The film formation chamber 132 is a spare film formation chamber.

A substrate where at least up to a cathode is introduced into thetransport chamber 114, and stored in the substrate stock chambers 130 aand 130 b or transferred to the delivery chamber 141 through thetransport chamber 108 and the delivery chamber 111. It is preferablethat the transport chamber 114, the substrate stock chambers 130 a and130 b, and the delivery chamber 141 are kept under reduced pressure.

Then, the first substrate transferred to the delivery chamber 141 istransferred to an attachment chamber 144 by a transport mechanism 148installed in the transport chamber 147.

A second substrate that serves as a sealing substrate is previouslyprovided with columnar or wall-shaped structures. The second substrateis introduced into a substrate loading chamber 117, and heated thereinunder reduced pressure so that degasification is performed. The secondsubstrate is then transferred to a pretreatment chamber 146 providedwith an UV irradiation mechanism by the transport mechanism 148 which isinstalled in the transport chamber 147. In the pretreatment chamber 146,the surface of the second substrate is treated by UV irradiation. Thesecond substrate is then transferred to the seal formation chamber 145to form a sealing material thereon. The seal formation chamber 145 isprovided with a dispenser device or an ink-jet device. The sealformation chamber 145 may also be provided with a baking unit or an UVirradiation unit to pre-cure the sealing material. After pre-curing thesealing material in the seal formation chamber 145 for forming a sealingmaterial, a filler is dropped in a region surrounded by the sealingmaterial.

The second substrate is also transferred to the attachment chamber 144by the transport mechanism 148.

In the attachment chamber 144, after reducing pressure in the treatmentchamber, the first and second substrates are attached to each other. Atthis moment, the first and second substrates are attached to each otherby moving an upper plate or a lower plate up and down. Upon attachingthe two substrates under reduced pressure, the spacing between thesubstrates is kept precisely due to the columnar or wall-shapedstructures that have been provided on the second substrate. The columnaror wall-shaped structures also have a function of dispersing pressureapplied to the substrates, which is important, to prevent breakage ofthe substrates.

Alternatively, the filler may be dropped in the region surrounded by thesealing material in the attachment chamber 144, instead of the sealformation chamber 145.

Instead of reducing the pressure within the entire treatment chamber,after making a space between the plates airtight by moving the upper andlower plates vertically, the airtight space therebetween may be degassedby a vacuum pump through a hole that is provided in the lower plate toreduce the pressure. In this case, since the volume to be depressurizedis smaller as compared with the case of depressurizing the entiretreatment chamber; thus, the pressure within the airtight space can bereduced at a short time.

Further, a transparent window may be provided in one of the upper andlower plates such that the sealing material may be cured by beingirradiated with light that passes through the transparent window whilemaintaining the spacing between the upper and lower plates and attachingthe substrates to each other.

The pair of substrates, which is temporarily attached to each other, istransferred to the curing chamber 143 by the transport mechanism 148. Inthe curing chamber 143, the sealing material is completely cured bylight irradiation or heat treatment.

The pair of substrates is thus transferred to the unloading chamber 119by the transport mechanism 148. The pressure within the unloadingchamber 119, which has been kept under reduced pressure, is increased upto atmospheric pressure, and then the pair of attached substrates istaken out therefrom. Consequently, the sealing step for maintaining theconstant gap between the substrates is completed.

This embodiment mode can be freely combined with any of Embodiment Mode1, Embodiment Mode 2, or Embodiment Mode 3.

Embodiment Mode 5

Here, experimental results of contact resistance between a buffer layerand an anode, and measured results of light extraction efficiency willbe described.

A voltage of 6V was applied to a light emitting element having a 2 mm×2mm light emitting area, in which an anode formed with a TiN film, abuffer layer (a layer in which α-NPD and molybdenum oxide are mixed), alight emitting layer, and a cathode were provided in order. Then, acurrent value of 0.313 mA was obtained by measurement. Thus, the contactresistance between the TiN film and the buffer layer is good. Theluminance of the element was 501 cd/m²

An anode formed with a Ti film, a buffer layer (a layer in which α-NPDand molybdenum oxide are mixed), a light emitting layer, a cathode wereprovided in order. The current value was measured in the same manner,and a current value of 0.249 mA was obtained. Thus, the contactresistance between the Ti film and the buffer layer is also good. Theluminance of the element was 577 cd/m²

Further, current value of the case where an Al film (containing a minuteamount of Ti) is used as an anode was measured, and the value of 0.015mA was obtained. Thus, contact resistance of the Al film and the bufferlayer is not as good as one between the buffer layer and the Ti film orthe TiN film. The luminance of the element was 51 cd/m².

Further, if a translucent electrode such as a thin Ag electrode is usedas a cathode, strong interference occurs; thus, the light extractionefficiency can be changed in various forms.

The result of the measured result of the relative luminance of the casewhere 6 V is applied to an anode of TiN is shown in FIG. 8. The resultshows that the same relative luminance can be obtained by optimizing thethickness of the buffer layers depending on each light emission color.Incidentally, the element structure of FIG. 9 was used for themeasurement.

This embodiment mode can be freely combined with Embodiment Mode 1,Embodiment Mode 2, or Embodiment Mode 3.

Embodiment Mode 6

Semiconductor devices and electronic devices according to the presentinvention include cameras such as video cameras or digital cameras,goggle-type displays (head mounted displays), navigation systems, audioreproduction devices (such as car audio components or audio components),personal computers, game machines, mobile information terminals (mobilecomputers, cellular phones, mobile game machines, electronic books, andthe like), image reproduction devices equipped with a recording medium(specifically, devices which can reproduce content of a recording mediumsuch as Digital Versatile Disk (DVD) and have a display for displayingthe image), and the like. Specific examples of the electronic devicesare shown in FIGS. 10A to 10D and FIG. 11.

FIG. 10A shows a digital camera, which includes a main body 2102, adisplay area 2102, an imaging portion, operation keys 2104, a shutter2106, and the like. FIG. 10A shows the digital camera seen from thedisplay area 2102 side, and the imaging portion is not shown in FIG.10A. According to the present invention, a digital camera can bemanufactured through a process with reduced manufacturing cost.

FIG. 10B shows a notebook personal computer, includes a main body 2201,a casing 2202, a display area 2203, a keyboard 2204, an externalconnection port 2205, a pointing mouse 2206, and the like. According tothe present invention, a notebook personal computer can be manufacturedthrough a process with reduced manufacturing cost.

FIG. 10C shows a portable image reproducing device, which includes arecording medium (specifically, a DVD player), which includes a mainbody 2401, a casing 2402, a display area A 2403, a display area B 2404,a recording medium (such as a DVD) reading portion 2405, operation keys2406, a speaker portion 2407, and the like. The display area A 2403mainly displays image information and the display area B 2404 mainlydisplays text information. The category of such an image reproducingdevice provided with a recording medium includes an electronic gamemachine (typically, a home game machine), and the like. According to thepresent invention, an image reproducing device can be manufacturedthrough a process with reduced manufacturing cost.

FIG. 10D shows a display device, which includes a casing 1901, a support1902, a display area 1903, a speaker portion 1904, a video inputterminal 1905, and the like. This display device is manufactured using athin film transistor formed in accordance with a manufacturing methoddescribed in any one of the embodiment modes described above for thedisplay area 1903 and the driver circuit. Display devices include liquidcrystal display devices, light-emitting devices, and the like.Specifically, all types of display devices for displaying information,for example, display devices for computers, display devices forreceiving television broadcasting, and display devices for advertisementare included. According to the present invention, a display device, inparticular, a large size display device having a large screen of 22 to50 inches can be manufactured through a process with reducedmanufacturing cost.

In the cellular phone 900 shown in FIG. 11, a main body (A) 901including operation switches 904, a microphone 905, and the like isconnected to a main body (B) 902 including a display panel (A) 908, adisplay panel (B) 909, a loudspeaker 906, and the like, using a hinge910 which makes the cellular phone foldable. The display panel (A) 908and the display panel (B) 909 are housed in a casing 903 of the mainbody (B) 902 together with a circuit board 907. Pixel areas of thedisplay panel (A) 908 and the display panel (B) 909 are disposed suchthat they are visible through an opening formed in the casing 903.

As to the display panel (A) 908 and the display panel (B) 909, thespecification such as the number of pixels can be appropriatelydetermined in accordance with the functions of the cellular phone 900.For example, the display panel (A) 908 and the display panel (B) 909 canbe combined as a main screen and a sub-screen, respectively.

The display panel (A) 908 has a structure which can be AC operated asshown in any one of Embodiment Modes 1 to 5. According to the presentinvention, a mobile information terminal can be manufactured through aprocess with reduced manufacturing cost.

The cellular phone according to this embodiment mode can be changed invarious modes depending on the functions or the use thereof. Forexample, a cellular phone with camera may be manufactured byimplementing an imaging element in part of the hinge 910, for example.Even when the operation switches 904, the display panel (A) 908, and thedisplay panel (B) 909 are housed in one casing, the above-describedeffects can be obtained. Further, similar effects can be obtained evenwhen the structure of this embodiment mode is applied to an informationdisplay terminal provided with a plurality of display areas.

As described above, various types of electronic devices can be completedby using a manufacturing method or a structure for implementing thepresent invention, in other words, any one of manufacturing methods orstructures in Embodiment Modes 1 to 5.

In accordance with the present invention, an active matrix lightemitting device can be manufactured in a shorter time with high yield atlow cost compared with conventional ones.

1. A light emitting device comprising: a substrate having an insulatingsurface; a semiconductor layer of a thin film transistor over thesubstrate; a first electrode directly connected to the semiconductorlayer; an insulator covering an end portion of the first electrode; abuffer layer over the first electrode; a layer containing an organiccompound over the buffer layer; and a second electrode over the layercontaining an organic compound, wherein the first electrode comprises afirst layer in direct contact with the semiconductor layer and with thebuffer layer, and a second layer formed over of the first layer, whereinthe insulator is interposed between the second layer and the bufferlayer, wherein the first layer is continuous from the semiconductorlayer to the buffer layer and is interposed between the second layer andthe semiconductor layer, wherein the first electrode has a first regionand a second region having a different number of layers from the firstregion, wherein a step is formed by an end part of the second layerbetween the first region and the second region, and wherein the step iscovered with the insulator.
 2. A light emitting device according toclaim 1, wherein the buffer layer is provided in contact with the firstregion of the first electrode.
 3. A light emitting device according toclaim 1, wherein the first electrode includes the first region having ametal film including two layers and the second region having a metalfilm including four layers.
 4. A light emitting device according toclaim 1, wherein the first electrode includes the first region having ametal film including two layers and the second region having a metalfilm including three layers.
 5. A light emitting device according toclaim 1, wherein the first electrode includes the first region having asingle layer metal film and the second region having a metal filmincluding two or more layers.
 6. A light emitting device according toclaim 1, wherein the first electrode has a film mainly containing anelement selected from the group consisting of Ti, TiN, TiSi_(X)N_(Y),Al, Ag, Ni, W, WSi_(X), WN_(X), WSi_(X)N_(Y), Ta, TaN_(X),TaSi_(X)N_(Y), NbN, MoN, Cr, Pt, Zn, Sn, In, and Mo; or an alloy or acompound mainly containing the above element; or a stack of the films.7. A light emitting device according to claim 1, wherein area of a lightemitting area of one light emitting element is smaller than area of thefirst region.
 8. A light emitting device according to claim 1, whereinthe buffer layer includes a composite material of an organic compoundand an inorganic compound, and the inorganic compound is one or moreselected from the group consisting of titanium oxide, zirconium oxide,hafnium oxide, vanadium oxide, niobium oxide, tantalum oxide, chromiumoxide, molybdenum oxide, tungsten oxide, manganese oxide, and rheniumoxide.
 9. A light emitting device according to claim 1, wherein thebuffer layer includes a composite material containing an organiccompound having hole transporting characteristics and an inorganiccompound.
 10. A light emitting device according to claim 1, wherein thesecond electrode is a light-transmitting conductive film.
 11. A lightemitting device according to claim 1, wherein the light emitting deviceis a video camera, a digital camera, a navigation system, a personalcomputer, a game machine, or an information terminal.
 12. A lightemitting device comprising: a substrate having an insulating surface; asemiconductor layer of a thin film transistor over the substrate; afirst electrode electrically connected to the semiconductor layer; aninsulator covering an end portion of the first electrode; a buffer layerover the first electrode; a layer containing an organic compound overthe buffer layer; and a second electrode over the layer containing anorganic compound, wherein the first electrode comprises a first layer indirect contact with the semiconductor layer and with the buffer layer,and a second layer formed over of the first layer, wherein the insulatoris interposed between the second layer and the buffer layer, wherein thefirst layer is continuous from the semiconductor layer to the bufferlayer and is interposed between the second layer and the semiconductorlayer, wherein the first electrode has a first region and a secondregion having a different number of layers from the first region,wherein a step is formed by an end part of the second layer between thefirst region and the second region, and wherein the step is covered withthe insulator.
 13. A light emitting device according to claim 12,wherein the light emitting device includes a pixel area provided with aplurality of light emitting elements and a driver circuit having aplurality of thin film transistors, and the driver circuit includes awiring having a same stack as the second region.
 14. A light emittingdevice according to claim 12, wherein the buffer layer is provided incontact with the first region of the first electrode.
 15. A lightemitting device according to claim 12, wherein the first electrodeincludes the first region having a metal film including two layers andthe second region having a metal film including four layers.
 16. A lightemitting device according to claim 12, wherein the first electrodeincludes the first region having a metal film including two layers andthe second region having a metal film including three layers.
 17. Alight emitting device according to claim 12, wherein the first electrodeincludes the first region having a single layer metal film and thesecond region having a metal film including two or more layers.
 18. Alight emitting device according to claim 12, wherein the first electrodehas a film mainly containing an element selected from the groupconsisting of Ti, TiN, TiSi_(X)N_(Y), Al, Ag, Ni, W, WSi_(X), WN_(X),WSi_(X)N_(Y), Ta, TaN_(X), TaSi_(X)N_(Y), NbN, MoN, Cr, Pt, Zn, Sn, In,and Mo; or an alloy or a compound mainly containing the above element;or a stack of the films.
 19. A light emitting device according to claim12, wherein area of a light emitting area of one light emitting elementis smaller than area of the first region.
 20. A light emitting deviceaccording to claim 12, wherein the buffer layer includes a compositematerial of an organic compound and an inorganic compound, and theinorganic compound is one or more selected from the group consisting oftitanium oxide, zirconium oxide, hafnium oxide, vanadium oxide, niobiumoxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide,manganese oxide, and rhenium oxide.
 21. A light emitting deviceaccording to claim 12, wherein the buffer layer includes a compositematerial containing an organic compound having hole transportingcharacteristics and an inorganic compound.
 22. A light emitting deviceaccording to claim 12, wherein the second electrode is alight-transmitting conductive film.
 23. A light emitting deviceaccording to claim 12, wherein the light emitting device is a videocamera, a digital camera, a navigation system, a personal computer, agame machine, or an information terminal.
 24. A light emitting devicecomprising: a substrate having an insulating surface; a semiconductorlayer of a thin film transistor over the substrate; a first electrodedirectly connected to the semiconductor layer; an insulator covering anend portion of the first electrode; a buffer layer over the firstelectrode; a layer containing an organic compound over the buffer layer;and a second electrode which transmits light over the layer containingan organic compound, wherein the first electrode comprises a first layerin direct contact with the semiconductor layer and with the bufferlayer, and a second layer formed over of the first layer, wherein theinsulator is interposed between the second layer and the buffer layer,wherein the first layer is continuous from the semiconductor layer tothe buffer layer and is interposed between the second layer and thesemiconductor layer, wherein the first electrode has a first region anda second region having more layers than the first region, wherein a stepis formed by an end part of the second layer between the first regionand the second region, and wherein the step is covered with theinsulator.
 25. A light emitting device according to claim 24, whereinthe buffer layer is provided in contact with the first region of thefirst electrode.
 26. A light emitting device according to claim 24,wherein the first electrode has a film mainly containing an elementselected from the group consisting of Ti, TiN, TiSi_(X)N_(Y), Al, Ag,Ni, W, WSi_(X), WN_(X), WSi_(X)N_(Y), Ta, TaN_(X), TaSi_(X)N_(Y), NbN,MoN, Cr, Pt, Zn, Sn, In, and Mo; or an alloy or a compound mainlycontaining the above element; or a stack of the films.
 27. A lightemitting device according to claim 24, wherein area of a light emittingarea of one light emitting element is smaller than area of the firstregion.
 28. A light emitting device according to claim 24, wherein thebuffer layer includes a composite material of an organic compound and aninorganic compound, and the inorganic compound is one or more selectedfrom the group consisting of titanium oxide, zirconium oxide, hafniumoxide, vanadium oxide, niobium oxide, tantalum oxide, chromium oxide,molybdenum oxide, tungsten oxide, manganese oxide, and rhenium oxide.29. A light emitting device according to claim 24, wherein the bufferlayer includes a composite material containing an organic compoundhaving hole transporting characteristics and an inorganic compound. 30.A light emitting device according to claim 24, wherein the lightemitting device is a video camera, a digital camera, a navigationsystem, a personal computer, a game machine, or an information terminal.31. A light emitting device comprising: a substrate having an insulatingsurface; a semiconductor layer of a thin film transistor over thesubstrate; a first electrode electrically connected to the semiconductorlayer; an insulator covering an end portion of the first electrode; abuffer layer over the first electrode; a layer containing an organiccompound over the buffer layer; and a second electrode which transmitslight over the layer containing an organic compound, wherein the firstelectrode comprises a first layer in direct contact with thesemiconductor layer and with the buffer layer, and a second layer formedover of the first layer, wherein the insulator is interposed between thesecond layer and the buffer layer, wherein the first layer is continuousfrom the semiconductor layer to the buffer layer and is interposedbetween the second layer and the semiconductor layer, wherein the firstelectrode has a first region and a second region having more layers thanthe first region, wherein a step is formed by an end part of the secondlayer between the first region and the second region, and wherein thestep is covered with the insulator.
 32. A light emitting deviceaccording to claim 31, wherein the light emitting device includes apixel area provided with a plurality of light emitting elements and adriver circuit having a plurality of thin film transistors, and thedriver circuit includes a wiring having a same stack as the secondregion.
 33. A light emitting device according to claim 31, wherein thebuffer layer is provided in contact with the first region of the firstelectrode.
 34. A light emitting device according to claim 31, whereinthe first electrode has a film mainly containing an element selectedfrom the group consisting of Ti, TiN, TiSi_(X)N_(Y), Al, Ag, Ni, W,WSi_(X), WN_(X), WSi_(X)N_(Y), Ta, TaN_(X), TaSi_(X)N_(Y), NbN, MoN, Cr,Pt, Zn, Sn, In, and Mo; or an alloy or a compound mainly containing theabove element; or a stack of the films.
 35. A light emitting deviceaccording to claim 31, wherein area of a light emitting area of onelight emitting element is smaller than area of the first region.
 36. Alight emitting device according to claim 31, wherein the buffer layerincludes a composite material of an organic compound and an inorganiccompound, and the inorganic compound is one or more selected from thegroup consisting of titanium oxide, zirconium oxide, hafnium oxide,vanadium oxide, niobium oxide, tantalum oxide, chromium oxide,molybdenum oxide, tungsten oxide, manganese oxide, and rhenium oxide.37. A light emitting device according to claim 31, wherein the bufferlayer includes a composite material containing an organic compoundhaving hole transporting characteristics and an inorganic compound. 38.A light emitting device according to claim 31, wherein the lightemitting device is a video camera, a digital camera, a navigationsystem, a personal computer, a game machine, or an information terminal.39. A light emitting device according to claim 1, wherein the bufferlayer includes a composite material of an organic compound and aninorganic compound, and the inorganic compound shows electron acceptingcharacteristics with respect to the organic compound.
 40. A lightemitting device according to claim 12, wherein the buffer layer includesa composite material of an organic compound and an inorganic compound,and the inorganic compound shows electron accepting characteristics withrespect to the organic compound.
 41. A light emitting device accordingto claim 24, wherein the buffer layer includes a composite material ofan organic compound and an inorganic compound, and the inorganiccompound shows electron accepting characteristics with respect to theorganic compound.
 42. A light emitting device according to claim 31,wherein the buffer layer includes a composite material of an organiccompound and an inorganic compound, and the inorganic compound showselectron accepting characteristics with respect to the organic compound.